The objective of this project is to characterize dose-response relationships and toxicity of nitromethane administered by inhalation to rats and mice in 14-day repeated-dose, 90-day subchronic and 2-year chronic studies. Animals will be exposed for 6 hours per day, 5 days per week for 14 and 90 days or 2 years. At the end of each study, all animals will be given gross and microscopic histopathologic evaluations. Hematology, clinical chemistry, and sperm morphology/vaginal cytology will be performed in the 90-day study. A 65-week interim sacrifice, including hematology and histopathology will be performed in the chronic study. The results of each study will be used by NTP to establish doses to be used in the next study (i.e., the 14-day results for the 90-day study; the 90-day results for the chronic study).